On 2018-07-24 17:00:09 [+0200], Peter Zijlstra wrote:
> On Tue, Jul 24, 2018 at 04:35:09PM +0200, Sebastian Andrzej Siewior wrote:
> > I doubt that there any need to set ->active_mm. It is used by the
> > scheduler to keep track of the "currently used mm" so it can reuse one
> > for the kernel thread which does not own one and take a reference on it
> > so it does not go away while the thread (that borrows it) is active.
>
> > void efi_switch_mm(struct mm_struct *mm)
> > {
> > - task_lock(current);
> > efi_scratch.prev_mm = current->active_mm;
> > - current->active_mm = mm;
> > switch_mm(efi_scratch.prev_mm, mm, NULL);
> > - task_unlock(current);
> > }
>
> I think that's broken. Take for instance stuff like
> perf_callchain_user32() -> get_segment_base(). That looks at active_mm
> to get at the current LDT.
right. I saw that briefly not sure why I dropped it. I have no idea
where the LDT points to but it probably sense to return EFI's version of
it.
> Now, I'm not saying the whole perf vs EFI thing isn't already terminally
> wrecked, but the rule is that active_mm really should point at the
> current active mm, and the above breaks that.
Right. Even if we not perform a context switch. Okay. Will update that
part.
Sebastian
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